DAL's February 11 puts were popular on Thursday

Put volume ramped up on Delta Air Lines, Inc. (NYSE:DAL - 12.80) on Thursday, with the contracts trading at three times their average daily pace. Of the roughly 17,000 put contracts that changed hands yesterday, 5,350 did so at DAL's February 11 strike. Nearly all of these went off at the ask price, implied volatility rose 3.1 percentage points, and open interest added almost 5,200 contracts overnight -- pointing to buy-to-open activity.

In order for these out-of-the-money puts to be profitable, the stock needs to slide below breakeven at $10.76 (the strike minus the volume-weighted average price [VWAP] of $0.24) by the close on Feb. 15, at which point the options will expire. This is a steep 19% slide from DAL's current price.

Widening the scope reveals that traders have been upping their bearish exposure with some rapidity of late. The stock's 10-day International Securities Exchange (ISE)/Chicago Board Options Exchange (CBOE)/NASDAQ OMX PHLX (PHLX) put/call volume ratio of 0.95 ranks higher than 85% of other such readings taken in the past year, suggesting puts have been bought to open over calls at a faster-than-usual clip in recent weeks.

The bearish bias among options players is a bit puzzling considering DAL is up roughly 60% on a year-over-year basis. Additionally, the stock has outperformed the broader S&P 500 Index (SPX) by more than 21 percentage points during the past 40 sessions. More recently, the equity has enjoyed a push higher from its 10-day moving average, which helped lift DAL to a two-year peak of $12.94 in today's session.

In light of this technical prowess, the recent trend toward puts could simply be shareholders protecting profits against a potential pullback. If this was the case in Thursday's session, the purchasers of the February 11 puts paid a pretty penny for their options insurance. Implied volatility at this strike is currently elevated relative to the stock's 40-day historical (realized) volatility (45% vs. 33.9%), meaning premiums are a bit pricier than usual.